Desktop Project Part 10: The crescent and the plume

By Phil Plait | April 4, 2012 11:00 am

[Over the past few weeks, I've collected a metric ton of cool pictures to post, but somehow have never gotten around to actually posting them. Sometimes I was too busy, sometimes too lazy, sometimes they just fell by the wayside... but I decided my computer's desktop was getting cluttered, and I'll never clean it up without some sort of incentive. I've therefore made a pact with myself to post one of the pictures with an abbreviated description every day until they're gone, thus cleaning up my desktop, showing you neat and/or beautiful pictures, and making me feel better about my work habits. Enjoy.]

With planetary pictures, angle is everything. If you have your back to the Sun and face your target, it’s fully lit, and looks like a disk. But if you go around to the other side, and put your target between you and the Sun, it becomes a crescent. Get the angle just right, and that crescent gets very thin…

… which is a view of Saturn’s moon Enceladus we can never get from Earth, but one that the Cassini spacecraft gets all the time. And it’s way, way cool:

[Click to encronosenate.]

But there’s an added bonus here, one that makes this picture that much more amazing: that fuzz at the bottom? Those are enormous geysers, towering sprays of water blasting out of cracks in the surface of the moon and reaching upward for hundreds of kilometers!

We’ve seen the geysers before, and in fact Cassini has flown through them to find out what they’re made of (turns out water laced with lots of organic goodness like acetylene, formaldehyde, and much more). They’re very dim, but easy to see when backlit by the Sun like this.

So we know Enceladus must have liquid water under its surface, to feed these geysers. But is it local, like a subsurface lake, or is the ice of the moon floating on a global ocean? New studies of the cracks from which the geysers emanate seem to indicate the water is everywhere! The geysers are formed from gravitational stress when the moon nears Saturn in its orbit, and the size and shape of the cracks really make it look like the water source is a global ocean, like Jupiter’s moon Europa.

Isn’t that amazing? We can learn a lot about a tiny, icy, backlit world, just by tasting its water.

Image credit: NASA/JPL-Caltech/Space Science Institute


Related Posts:

- Enceladus on full afterburner
- Life’s cauldron may be bubbling underneath Enceladus
- Enceladus!
- Enceladus does and does not have a global ocean

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (7)

  1. twotif

    Those are some beautiful pictures. I remember as a child, that everyone seemed to think that all the other bodies in our solar system were geologically inactive. OOOOOOOOPS!!

  2. jrpowell

    That’s no Death Star! ;^)

  3. Chuck Messer

    “The Fountains of Enceladus”. It sounds like the title of a novel.

    Chuck

  4. Taste is not a sense that astronomers use often. I used to say that Earth was the only planet that you can taste. However, we have meteorites from the Moon and Mars…

    Enceladus looks like a planet in this image. It’s round. The IAU’s ‘planet’ definition has fuzzy bits about planet dynamics, easy to reject. The press keeps saying it’s small. But 500 km is big enough to crush to a sphere, at least for some materials. I think i have to agree with Lucas, “That’s no moon.”

  5. Randy A.

    This is a seriously cool picture! Thanks for sharing it with us!

  6. @2. jrpowell : “That’s no Death Star! ;^)

    No, that’d be Mimas – another Saturnian moon with a distinct resemblance! ;-)

    (Click on my name for image via APOD.)

    @4. Stephen :

    Taste is not a sense that astronomers use often. I used to say that Earth was the only planet that you can taste. However, we have meteorites from the Moon and Mars…

    I’m pretty sure I read somewhere – but can’t quite recall where, sorry – that somebody has actually eaten a small quantity of lunar dust that they were sent by one of the Apollo Moon-walkers.

    Actually, the lunar dust apparently got everywhere throughout the returning Apollo spacecraft quarters so its likely that all the Moonwalkers from Neil Armstrong to Gene Cernan ingested some amount of Moondust. :-)

    Enceladus looks like a planet in this image. It’s round. The IAU’s ‘planet’ definition has fuzzy bits about planet dynamics, easy to reject. The press keeps saying it’s small. But 500 km is big enough to crush to a sphere, at least for some materials. I think i have to agree with Lucas, “That’s no moon.”

    I think it makes sense to say that a Moon which orbits another planet isn’t *itself* another planet but instead is a moon or natural satellite unless that body is about half the size of the size of the planet it orbits in which case “double planet” status seems to make sense for both worlds.

    But if Enceladus wasn’t orbiting Saturn then I’d have no problem calling it a planet.

    @1. twotif :

    Those are some beautiful pictures. I remember as a child, that everyone seemed to think that all the other bodies in our solar system were geologically inactive. OOOOOOOOPS!!

    Pre-Voyager Io fly -by obviously.

    Of course, there were lots of odd things we used to think about how the other planets in our solar system were – canals on Mars, soda seas, oil oceans and dinosuar-time-like swamps on Venus being just a few of them. Wondre what will surprise us inthe future and yet seem obvious to our descendents in a hundred plus years time? ;-)

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